Another interesting feature of this passage is that it is the friend who hears the cell phone, not the owner of the phone. How many times have you had to point out to someone that their phone was going off?

Heinlein fans should also note the "pommel phone" in his excellent 1951 novel Between Planets:

A few hundred yards further on Lazy [the horse] shied again, not from a snake this time but from an unexpected noise. Don pulled him in and spoke severely. "You bird-brained butterball! When are you going to learn not to jump when the telephone rings?"